Internally damped rotatable storage article

ABSTRACT

The present invention provides a method for internally damping a rotatable storage article which is subject to resonant vibrations. More specifically, the present invention provides a method of improving the damping properties of a rotatable storage article by introducing a viscoelastic material as an inner layer(s) of the rotatable storage article. The invention also provides the damped rotatable storage articles themselves.

FIELD OF THE INVENTION

The present invention relates to a method for internally damping arotatable storage article which is subject to resonant vibrations. Morespecifically, the present invention relates to a method of improving thedamping properties of a rotatable storage article by introducing aviscoelastic material as an inner layer(s) of the rotatable storagearticle. The invention also relates to the damped rotatable storagearticles themselves.

BACKGROUND OF THE INVENTION

Periodic or random vibrations or shocks can excite the resonantfrequencies in a rotatable storage article which can be problematic dueto the resultant formation of undesirable stresses, displacements,fatigue, and even sound radiation. Such undesirable vibrations or shocksare typically induced by external forces and can be experienced by awide variety of articles and under a variety of conditions. For example,resonant vibrations can cause excessive vertical displacement of artoptical disk's surface during operation which may lead to poor laserfocus. Proper laser focus is a key to optimum write/readcharacteristics, signal quality, and tracking ability.

Various techniques have been used to reduce vibrational and shockeffects (stresses, displacements, etc.) on storage articles. Three basictechniques to reduce vibration and shock effect include

1) adding stiffness or mass to the rotatable storage article so that theresonant frequencies of the rotatable storage article are not excited bya given excitation source,

2) isolating the rotatable storage article from the excitation so thevibrational or shock energy does not excite the rotatable storagearticle's resonant frequencies, and

3) damping the rotatable storage article so that given excitations do noresult in excessive negative effects at the resonant frequencies of therotatable storage article.

An isolation technique for limiting vibration transmission is describedin U.S. Pat. No. 4,870,429 issued Sep. 26, 1989. A single-sided ordouble-sided optical disk structure is described which includes twosheets of substrate bonded to each other with a foam spacer interposedbetween the two substrates to restrict or isolate the vibrations causedby external forces. The spacer is made from an elastomeric foam materialand is positioned between the two substrates to restrict thetransmission of such forces (e.g. vibrations or shocks). The thicknessof the spacer is stated to be preferably not less than 0.2 mm, morepreferably not less than 0.4 mm, because when the thickness is too smallthe effect of the spacer to restrict or isolate forces is not exhibitedsufficiently. Such a system adds to the overall size of the rotatablestorage article and may be impractical where close positioning of thearticle to other structures is desired.

Two types of surface or external damping treatments which can be used toreduce shock or vibration impact on rotatable articles are: (1) freelayer damping treatments; and (2) constrained layer damping treatments.Both of these damping treatments, Dan provide high levels of damping toa structure, i.e., dissipation of undesirable vibrations, withoutsacrificing the stiffness of the structure. The use of viscoelasticmaterials as exterior surface damping treatments is described in EP0507515 published Oct. 7, 1992. Examples of additional surface orexternal damping techniques are described, for example, in U.S. Pat.Nos. 2,819,032 (issued Jan. 7, 1953); 3,071,217 (issued Jan. 1, 1963);3,078,969 (issued Feb. 26, 1963); 3,159,249 (issued Dec. 1, 1964); and3,160,549 (issued Dec. 8, 1964). All of the aforementioned dampingtechniques can add complexity and expense to the design of the rotatablestorage article, limit the amount of exterior article surface availablefor data storage, and can increase the overall size of the article.

Free layer damping; treatment is also referred to as "unconstrainedlayer" or "extensional damping" treatment. In this technique, dampingoccurs by applying a layer of viscoelastic damping material to one ormore exterior surfaces of the article to be damped. The material can beapplied to one or more exterior surfaces of the article to be damped.The mechanism by which this treatment method dissipates undesirableenergy, e.g., resonant vibrations, involves deformation. That is, whenthe article is subjected to cyclic loading, for example, the dampingmaterial is subjected to tension-compression deformation and dissipatesthe energy through an extensional strain mechanism.

Constrained layer damping treatment is also referred to as "sheardamping" treatment. For a given weight, this type of damping treatmentis generally more efficient than the free layer damping treatment. Inthis technique, damping occurs by applying a damper consisting of one ormore layers of viscoelastic damping material and one or more layers of ahigher tensile modulus material to one or more exterior surfaces of thearticle to be damped. That is, this damping technique is similar to thefree layer damping treatment wherein a viscoelastic material is appliedto one or more exterior surfaces of a structure, the difference beingthat the viscoelastic material is additionally constrained by a layerhaving a higher modulus than the viscoelastic material, e.g., a metallayer, in the constrained layer treatment. Energy dissipates from theviscoelastic damping material via a shear strain mechanism. The shearstrain results from constraints by the higher modulus constraining layerand the base structure.

Although these exterior surface damping techniques are used, the degreeof damping is oftentimes limited by thickness or spacing requirements aswell as application difficulties. Furthermore, the exterior damper mustbe applied to potential data storage surface areas, limiting informationstorage capability. In addition, external dampers can interfere withinformation retrieval from the storage article. Another disadvantage isthat the external damper may be subject to degradation by theenvironmental conditions in which it is used. As way of example, if arotatable storage article is desired to be a component in a size limitedapplication, such as hard disk drives for portable computer systems,computers, or calculators, the ability to adequately damp the rotatablestorage article by means of an "add-on" exterior surface damper may notbe possible due to overall thickness requirements to meet a "formfactor" requirement or the necessity of using the exterior surface fordata/information storage. Thus, an alternative approach is needed todamp vibrational or shock energy without adversely affecting the overallsize or thickness or available surface area of the rotatable storagearticle.

SUMMARY OF THE INVENTION

We have found such an alternative approach. The present inventionprovides an internally damped rotatable storage article.

The term "rotatable storage article" as used herein refers to a mediathat has information stored on it and/or which is capable of storinginformation. The article is typically capable of being rotated in somemanner that allows the data stored on the article to be passed by a reador write element to allow reading of information from the article, orwriting of information on the article, or both. Examples of storagearticles include rigid disk drive disks, optical disks, compact disks(CDs), magneto-optical disks, records, drums, floppy disks and the like.

The present invention also provides a method of improving the vibrationdamping characteristics of a rotatable storage article by providing aninternally damped rotatable storage article. The method typicallyinvolves incorporating one or more layers of a vibration dampingmaterial into the storage article typically by adding one layer or aplurality of layers of a damping material during the manufacture of therotatable storage article as an inner layer. The layer(s) may becontinuous or discontinuous. The discontinuous layer may be separated byspace(s) and/or a non-damping material. A continuous layer may comprisethe same damping material or different damping material adjacent to eachother, thereby forming a continuous surface.

The vibration damping material includes a viscoelastic material orcombination of different viscoelastic materials. Useful viscoelasticmaterials are those having a storage, modulus of at least about 1.0 psi(6.9×10³ Pascals) and a loss factor of at least about 0.01, at thetemperature and frequency of use. Advantageously and preferably, alayer(s) of the vibration damping material is placed in areas of highstrain energy as an inner layer(s) to provide improved damping in thedesired frequency and temperature range. The added damping layer(s)increases the vibrational damping, as measured by the system lossfactor, of the rotatable storage article or the structural material ofwhich it is made, by at least about 10% in at least one vibrationalmode. System loss factor is a measure of the damping in a structure.

In certain preferred embodiments, the vibration damping material alsoincludes an effective amount of a fibrous material. The vibrationdamping material preferably includes an amount of fibrous materialeffective to improve vibration damping of the article or the structuralmaterial of which the article is made by a factor of at least about twoin strain energy ratio of at least one vibrational mode. Typically, thisrequires incorporating about 3 to 60 wt % of the fibrous material intothe vibration damping material, based on the total weight of thevibration damping material. Preferably, the fibrous material is anonmetallic fibrous material, such as glass.

In another preferred embodiment, the vibration damping material alsoincludes an effective amount of a particulate material. The vibrationdamping material preferably includes an amount of particulate materialeffective to improve vibrational damping of the article or thestructural material of which the article is made by a factor of at leastabout two in strain energy ratio of at least one vibrational mode.Typically, this requires incorporating about 0.5 to 70 weight percent ofthe particulate material into the vibration damping material, based onthe total weight of the vibration damping material. Combinations ofparticulate and fibrous materials may be used, typically about 0.5 toabout 70 wt. % based on the total damping material. Additionally, incertain preferred embodiments, the vibration damping material thatprovides the significant portion of the damping for a given materiallayer also includes an effective amount of an epoxy resin (with orwithout the particulate or fibrous material) dispersed within thedamping material. The vibration damping material preferably includes anamount of epoxy resin effective to improve the mechanical integrity ofthe rotatable disk storage article or the structural material of whichthe rotatable disk storage article is made. The epoxy resin material mayoptionally having damping properties. An example of a suitable dampingmaterial incorporating an epoxy resin is disclosed in U.S. Pat. No.5,262,232 (issued Nov. 13, 1993), incorporated herein by reference.Typically, the amount of epoxy resin incorporated into the vibrationdamping material is about 0.5 to 95 weight percent, preferably about 5to about 50 weight percent, based on the total weight of the vibrationdamping material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic top view of a "disk type" rotatable storagearticle of the present invention having a continuous single layer of avibrational damping material placed near the center of the article'sthickness.

FIG. 2 is a schematic of a "disk type" rotatable storage article of thepresent invention showing a cross-section of the rotatable storagearticle of FIG. 1 having one layer of damping material.

FIG. 3 is a schematic of an alternative embodiment of the presentinvention showing a cross-section of a rotatable storage article havingtwo layers of damping material which are not exposed at the articleouter perimeter.

FIG. 4 is a schematic of an alternative embodiment of the presentinvention showing a cross-section of a rotatable storage article havinga single discontinuous layer of damping material which is not exposed atthe inner or outer perimeter of the article.

FIG. 4b is a schematic of an alternative embodiment of the presentinvention showing a cross-section of rotatable storage article having asingle discontinuous layer of damping material which is not exposed atthe inner or outer perimeter of the article.

FIG. 5 is a graph of frequency versus transfer function for Example 1and Comparative Example 2 identified as A and B, respectively.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method of improving damping propertiesof rotatable storage articles, and thereby solving vibration problems ina variety of applications where rotatable storage articles are exposedto vibration or shock. More specifically, the present invention providesa vibration and shock resistant internally damped rotatable storagearticle that uses a highly dissipative damping material, with a lossfactor of at least about 0.01 at a given frequency and temperature,preferably at least about 0.1. This damping material, when placed in therotatable storage article as inner layer(s), can be exposed tosignificant amounts of strain energy in various vibrational modes ofinterest and dissipates a portion of this vibrational energy as heat,thereby diminishing vibration and shock displacement oscillations. Thepresent invention functions so as to damp, i.e., reduce the vibrationalor shock amplitude or duration of, a wide variety of vibrational modes,e.g., bending, torsion, sway, and extensional modes, in a wide varietyof rotatable storage article designs and over a wide frequency andtemperature range. It can be applied to situations in which exteriorsurface treatments, such as constrained layer treatments, are typicallyused and are especially useful where overall size of the article isimportant.

The method of the present invention typically involves the incorporationof a vibration damping material as one or more interior layers of therotatable storage article laminate. The vibration damping material maybe layered in between the structural material, e.g., aluminum and italloys, polyester, ceramic, polycarbonate, glass, and/or vinyl, etc. ofthe rotatable storage article. Preferably, the laminated material hasthe damping material laminated, sprayed, silk screened, or cast onto oneor more layers of structural material. The damping material layer can becontinuous, or discontinuous. The final rotatable storage article designcan have the damping material encased around the edges using, forexample, metal or plastic or sealed with adhesive, tape, or by sonicbonding or the like so that the damping material is substantiallycompletely surrounded by, i.e., encased or enclosed within, thestructural material, which provides protection of the damping materialfrom environmental conditions. Alternately, the damping material can beexposed at the perimeter edges or cutouts within the rotatable storagearticle, which is preferred from a damping standpoint. The addition ofthe damping material into the laminate structure results in creating aninherently damped rotatable substrate laminate that can be furtherprocessed to add magnetic or optical recording coatings and an openingfor a hub or spindle.

The damping layer may substantially form a layer having about the samedimensions as the substrate layers between which it is sandwiched.Alternately, the layer may be of more limited dimensions and may besituated in an area of greatest vibrational stresses.

Typically, an amount of the damping material is present such that thedamping characteristics of the rotatable storage article are improved.Preferably, a sufficient amount of the vibration damping material isused such that the damping is improved by at least about 10% in at leastone vibrational mode. As a result of this technique, high mechanicalstrains are introduced into the damping material when the structure isexcited at one or more of its natural frequencies. A portion of theresulting mechanical strain energy in the damping material is thendissipated in the form of heat. The higher the strain energy in thedamping material, the more vibration energy is dissipated from therotatable storage article structure.

The placement of a partial layer of damping material in the rotatablestorage article can be influenced by whether the article edges aresealed. This can alter the stiffness of the rotatable storage articleand determine areas of greater vibrational activity for a givenvibrational or shock excitation of one of the modes of vibration in acertain area of the rotatable storage article. That is, the partialvibration damping material layer(s) are placed in the article where oneor more vibrational modes are active. By such placement, the amount ofstrain energy that is generated in the damping material used for therotatable storage article can be maximized. The identification of theselocations can be determined by one of skill in the art using modalanalysis or finite element analysis.

The rotatable storage article's structure damped by the method of thepresent invention can be prepared from any material suitable forrotatable storage article designs. Useful structural materials include,for example, metals such as aluminum and aluminum alloys; organicmaterials/resins such as polyester, polycarbonate and vinyl; andinorganic materials such as glass and ceramic. Additional materials suchas magnetic or optical coatings, wear resistant overcoats and lubricantsmay also be used for preparing the data storage surface(s) of thearticle of the invention.

The vibration damping material can include any material that isviscoelastic. A viscoelastic material is one that is viscous, andtherefore capable of dissipating energy, yet exhibits certain elasticproperties, and therefore capable of storing energy. That is, aviscoelastic material is an elastomeric material typically containinglong-chain molecules that can convert mechanical energy into heat whenthey are deformed. Such a material typically can be deformed, e.g.,stretched, by an applied load and gradually regain its original shape,e.g., contract, sometime after the load has been removed.

Suitable viscoelastic materials for use in the vibration dampingmaterials of the present invention have a storage modulus, i.e., measureof the energy stored during deformation, of at least about 1.0 psi(6.9×10³ Pascals). The storage modulus of useful viscoelastic materialscan be as high as 500,000 psi (3.45×10⁹ Pascals); however, typically itis about 10-2000 psi (6.9×10⁴ -1.4×10⁷ Pascals).

Suitable viscoelastic materials for use in the vibration dampingmaterials of the present invention have a loss factor, i.e., the ratioof energy loss to energy stored, of at least about 0.01. Preferably theloss factor is at least about 0.1, more preferably about 0.5-10, andmost preferably about 1-10, in the frequency and temperature range wheredamping is required (typically about 1-10,000 Hz and -40° to 100° C.This loss factor is a measure of the material's ability to dissipateenergy and depends on the frequency and temperature experienced by thedamping material. For example, for a crosslinked acrylic polymer, at afrequency of 100 Hz, the loss factor at 68° F. (20° C.) is about 1.0,while at 158° F. (70° C.) the loss factor is about 0.7.

Preferred viscoelastic materials are those that remain functional over awide range of temperatures, e.g., -40° F. (-40° C.) to 300° F. (149°C.). Most preferred viscoelastic materials are those that cover thebroadest temperature and frequency range at the desired minimum lossfactor and storage modulus to achieve acceptable damping of therotatable storage article, and do not experience a significantdegradation in properties due to long times at high temperatures orshort excursions beyond these high temperature levels.

Useful viscoelastic damping materials can be isotropic as well asanisotropic materials, particularly with respect to its elasticproperties. As used herein, an "anisotropic material" or "nonisotropicmaterial" is one in which the properties are dependent upon thedirection of measurement. Suitable viscoelastic materials includeurethane rubbers, silicone rubbers, nitrile rubbers, butyl rubbers,acrylic rubbers, natural rubbers, styrene-butadiene rubbers, and thelike. Other useful damping viscoelastic materials include polyesters,polyurethanes, polyamides, ethylene-vinyl acetate copolymers, polyvinylbutyral, polyvinyl butyral-polyvinyl acetate copolymers, epoxy-acrylateinterpenetrating networks and the like. Specific examples of usefulmaterials are disclosed or referenced in U.S. Pat. No. 5,183,863 (issuedFeb. 2, 1993), U.S. Pat. No. 5,262,232 (issued Nov. 16, 1993) and U.S.Pat. No. 5,308,887 (issued May 3, 1994), all of which are incorporatedherein by reference.

Examples of thermoplastic materials suitable for use as the vibrationdamping material in rotatable storage articles according to the presentinvention include, but are not limited to, those selected from the groupconsisting of polyacrylates, polycarbonates, polyetherimides,polyesters, polysulfones, polystyrenes, acrylonitrile-butadiene-styreneblockcopolymers, polypropylenes, acetal polymers, polyamides, polyvinylchlorides, polyethylenes, polyurethanes, and combinations thereof.

Useful viscoelastic materials can also be crosslinkable to enhance theirstrength. Such viscoelastics are classified as thermosetting resins.When the viscoelastic material is a thermosetting resin, then prior tothe manufacture of the damped storage article. The thermosetting resinis in a thermoplastic state. During the manufacturing process, thethermosetting resin is cured and/or crosslinked typically to a solidstate, although it could be a gel upon curing as long as the curedmaterial possesses the viscoelastic properties described above.Depending upon the particular thermosetting resin employed, thethermosetting resin can include a curing agent, e.g., catalyst, whichwhen exposed to an appropriate energy source (such as thermal energy)the curing agent initiates the polymerization of the thermosettingresin. Particularly preferred viscoelastic damping materials are thosebased on acrylates.

In general, any suitable viscoelastic material can be used. The choiceof viscoelastic material for a particular set of conditions, e.g.,temperature and frequency of vibration, etc., is within the knowledge ofone of skill in the art of viscoelastic damping. It is to be understoodthat blends of any of the foregoing materials can also be used.

In addition to the viscoelastic material, the vibration damping materialof certain preferred embodiments of tile present invention includes aneffective amount of a fibrous and/or particulate material. Herein, an"effective amount" of a fibrous material or particulate is an amountsufficient to impart at least improvement in desirable characteristicsto the viscoelastic material, but not so much as to give rise to anysignificant detrimental effect on the structural, magnetic, optical(e.g., degrade read/write capability), or electrical integrity of therotatable storage article in which the viscoelastic material isincorporated. Generally, the fibrous or particulate material is used inan amount effective to increase the strain energy ratio of a componentcontaining the same amount and type of viscoelastic material without thefibrous or particulate material. Generally, an increase in the strainenergy ratio of a factor of at least about two in at least onevibrational mode is desired. Typically, the amount of the fibrousmaterial in the viscoelastic material is within a range of about 3-60 wt%, preferably about 10-50 wt %, more preferably about 15-45 wt %, andmost preferably about 20-40 wt %, based on the total weight of thevibration damping material. Typically, the amount of the particulatematerial in the viscoelastic material is within a range of about 0.5-70wt %, preferably about 1-45 wt %, more preferably about 5-40 wt %, andmost preferably about 5-30 wt %, based on the total weight of thevibration damping material.

The fibrous material can be in the form of fibrous strands or in theform of a fiber mat or web, although fibrous strands are preferred. Thefibrous strands can be in the form of threads, cords, yarns, filaments,etc., as long as the viscoelastic material can wet the surface of thematerial. They can be dispersed randomly or uniformly in a specifiedorder. Preferably, the fibrous strands, i.e., fibers or fine threadlikepieces, have an aspect ratio of at least about 2:1, and more preferablyan aspect ratio within a range of about 2:1 to about 10:1. The aspectratio of a fiber is the ratio of the longer dimension of the fiber tothe shorter dimension.

The fibrous material can be composed of any material that increases thedamping capability of the viscoelastic material. Examples of usefulfibrous materials in applications of the present invention includemetallic fibrous materials, such as aluminum oxide, magnesium or steelfibers, as well as nonmetallic fibrous materials, such as fiberglass.Generally, high Young's modulus fibrous materials, i.e., those having amodulus of at least about 1,000,000 psi (6.9×10⁹ pascals), arepreferred. Most preferably, the fibrous material is nonmetallic. Thenonmetallic fibrous materials can be a variety of materials, including,but not limited to, those selected from the group consisting of glass,carbon, minerals, synthetic or natural heat resistant organic materials,and ceramic materials. Preferred fibrous materials for rotatable storagearticles of the present invention ate organic materials, glass, andceramic fibrous material.

By "heat resistant" organic fibrous material, it is meant that useableorganic materials should be sufficiently resistant to melting, orotherwise softening or breaking down under the conditions of manufactureand use of the rotatable storage article of the present invention.Useful natural organic fibrous materials include, but are not limitedto, those selected from the group consisting of wool, silk, cotton, andcellulose. Examples of useful synthetic organic fibrous materialsinclude, but are not limited to, those selected from the groupconsisting of polyvinyl alcohol, nylon, polyester, rayon, polyamide,acrylic, polyolefin, aramid, and phenol. The preferred organic fibrousmaterial for applications of the present invention is aramid fibrousmaterial. Such a material is commercially available from Dupont Co.,Wilmington, Del. under the tradenames of "Kevlar" and "Nomex".

Generally, any ceramic fibrous material is useful in applications of thepresent invention. An example of a ceramic fibrous material suitable forthe present invention is NEXTEL™ which is commercially available fromMinnesota Mining and Manufacturing Co., St. Paul, Minn. Examples ofuseful, commercially available, glass fibrous material are thoseavailable from PPG Industries, Inc. Pittsburgh, Pa., under the productname E-glass bobbin yarn; Owens Corning, Toledo, Ohio, under the productname "Fiberglass" continuous filament yarn; and Manville Corporation,Toledo, Ohio, under the product name "Star Rov 502" fiberglass roving.

Advantages can be: obtained through use of fibrous materials of a lengthas short as about 100 micrometers. The fibers are not limited in lengthbut much longer fibers may provide insufficient fiber interface andtherefore decreased shearing surfaces between fibers. The fiberthickness or diameter for typical fibrous material ranges from about atleast 5 micrometers. The thinner the fiber, the higher the surface areaof the fibrous material. Thus, preferred fibrous materials are verythin. The thickness of the fiber is also dependent upon the desiredthickness; of the overall damping material layer that will be used inthe rotatable storage article. Thus, many common fibers may not besuitable if the overall damping material thickness is relatively thin(e.g., 4-10 micrometers).

The particulate material useful in the invention can be in the form ofglass and ceramic bubbles or beads, flakes, or powder, as long as theviscoelastic can wet the surface of the material. The particulatematerial can vary in size, but should not be greater than the thicknessof the damping material layer. Preferably, the particulate material ison the size order of about 0.1 to about 5 micrometers and morepreferably about 0.1 to about 2 micrometers.

The particulate material can be composed of any material that increasesthe damping capability of the viscoelastic damping material.

Examples of usefill particulate materials in applications of the presentinvention include coated or uncoated glass and ceramic bubbles or beadssuch as thermally conductive bubbles, powders such as aluminum oxidepowder and aluminum nitride powder, silica, cured epoxy nodules, and thelike, i.e., those having a modulus of at least about 10,000 psi (6.9×10⁷Pascals), are preferred. More preferably, useful particulate materialshave a Young's modulus of about 100,000 psi (6.9×10⁸ Pascals), and mostpreferable are those with a modulus of at least 1,000,000 psi (6.9×10⁹Pascals). Blends of a particulate material and fibrous material can beused from about 0.5 wt % to about 70 wt % based on the weight % ofdamping material.

In addition to fibers and particulate material, the vibration dampingmaterial of the present invention can include additives such as fillers(e.g. talc, etc.), colorants, toughening agents, fire retardants,antioxidants, antistatic agents, and the like. Sufficient amounts ofeach of these materials can be used to effect the desired result.

The damped rotatable storage article of the invention utilizes thedamping of viscoelastic materials with a minimum impact on the rotatablestorage article structural geometry and stiffness. Thus, the rotatablestorage articles of the present invention are good candidates forproducts that require added vibration and shock resistance in tightgeometry applications and/or sensitive weight applications. In addition,the damped storage article allows storage (e.g., data, information,etc.) on one or both sides of the rotatable storage article, if desired,whereas an add-on free layer or constrained layer damper would limitstorage to one side of the article. Thinner articles may also bepossible, as the addition of damping material to an inner layer of thelaminate may eliminate the need for added stiffness or mass to helpreduce the effects of vibrations or shock.

The internally damped laminate of the present invention will be betterunderstood by reference to the following FIGS. 1-4.

FIG. 1 is a schematic of one embodiment of the present invention showinga top view of a rotatable disk storage article 1 having an interiorcontinuous single layer of a damping material. The rotatable storagearticle 1 has an overcoat 3a such as polycarbonate to protect theinformation storage layer, outer radius 7, and inner radius 5.

FIG. 2 is a schematic of one embodiment of the present invention showinga cross section of a rotatable disk storage article 1 of FIG. 1 takenalong line 2--2. The article 1 has a continuous layer of a dampingmaterial 8 bonded between supporting; structural materials 4a and 4b.The disk 1 also includes information storage layers 6a and 6b, andovercoat layers 3a and 3b.

FIG. 3 is a schematic of an alternative embodiment of the presentinvention showing a cross section of a rotatable storage article 10having two layers of damping material 12a and 12b, which are not exposedat the article outer perimeter. The damping layers 12a and 12b arepositioned between supporting structural material 14. The article 10,which has an inner radius 18 and an outer radius 20, also includesinformation storage layers 16a and 16b and overcoat layers 13a and 13b.

FIG. 4 is a schematic of an alternative embodiment of the inventionshowing a cross section of a rotatable storage article 30 having asingle discontinuous layer of damping material 32, which is not exposedat the article 30 outer perimeter. The damping layer 33 is made up ofadjacent sections of a first damping material 33 and a different dampingmaterial 35. Alternatively the material 35 could, for example representa nondamping material or even a space. The damping layer 32 is placedwithin supporting structural material 34. The article 30 which has aninner radius 36 and an outer radius 38 also includes information storagelayers 40a and 40b, as well as overcoat layers 39a and 39b.

FIG. 4b is a schematic of an alternative embodiment of the inventionshowing a cross section of a rotatable storage article 50 having asingle discontinuous layer of damping material 52, which is not exposedat the article 50 outer perimeter. The damping layer 52 is made up ofadjacent sections of a first damping material 53 and spaces 54. Thedamping layer 52 is placed within supporting structural material 56. Thearticle 50 which has an inner radius 57 and an outer radius 59 alsoincludes information storage layers 60a and 60b, as well as overcoatlayers 62a and 62b.

Those skilled in the art can select the best means to introduce thedamping material into a specific process based on the needs of the finaldamped laminate rotatable storage article and also limitations inprocessing capabilities of the laminate input materials.

The vibrational damping material can include a viscoelastic material ora combination of viscoelastic material with a fibrous or particulatematerial. It is to be understood that the vibration damping material caninclude a blend of viscoelastic materials as well as a variety ofdifferent fibrous or particulate materials. Blends of fibreous andparticulate material are also possible.

The desired thickness of the damping material is typically 0.002 mm to0.5 mm; preferably, 0.02 mm to 0.15 mm; and most preferably, 0.02 mm to0.05 mm. Typically, the thickness of the damping material is about 0.5to about 50% of the thickness of the article, more typically about 1 toabout 25%. The rotatable storage article of the invention typicallycontains at least 1 damping layer, more typically 1-3 layers, preferably1-2, most preferably 1 for reasons of simplicity of the storagearticle's manufacturing process and cost. Stiffness may be sacrificedwhen more than 1 layer is included. However, a wider temperature rangeof damping is possible when multiple layers of different dampingmaterials are included. The amount of damping material used can vary.Sufficient material should be used to obtain the desired damping effectwhile balancing the structural requirements of the article. Thevibration damping layer may be continuous or discontinuous. A continuouslayer may comprise the same material or adjacent sections of differentvibration damping materials, for example. A discontinuous layer maycomprise sections of damping material separated by nondamping materialand/or spaces, for example. When 2 or more layers are present the layersmay comprise the same or different damping material and each may becontinuous or discontinuous.

When the article contains a single layer of vibration damping materialpreferably the layer is positioned within the article at a distance ofat least about 5%, more preferably at least about 30% of the thicknessof the article from an upper and lower surface of the article. When thearticle has one layer of damping material most preferably it ispositioned equidistant from an upper surface of the article and a lowersurface of the article. When the article contains at least two layers ofvibration damping material preferably each damping material layer ispositioned within the article such that it is at least about 5% of thethickness of the article away from an upper and lower surface of thearticle and each vibration damping material layer is preferably at leastabout 5%, more preferably at least about 20% and most preferably atleast about 30% of the thickness of the article away from anothervibration damping layer.

The rotatable storage article of the present invention can be made byany suitable technique for creating rotatable storage articles asunderstood by those in the industry. These techniques are generallyknown to those of skill in the art. For example, a damped rotatablerigid disk for a disk drive application can be made by adding a singlelayer of a damping material 0.025 mm thick near the center of a disk bylaminating a layer of aluminum with a layer of suitable damping materialand as additional layer of aluminum. This laminate is then stamped witha tool to yield a disk that has an inner damping layer. The disk "blank"is further processed to define edge and surface requirements and a readand writable data storage surface is added. The finished dampedrotatable disk will have increased damping over the non-damped disk ofthe same process.

Examples of rotatable storage articles which may be damped internallyinclude but are not limited to those selected from the group consistingof magnetic rotatable storage articles such as rigid disks, floppydisks, and drums; optical rotatable storage articles such as compactdisks, optical disks, and drums; magneto optical rotatable storagearticles such as compact disks, optical disks, drums; and mechanicalrotatable storage articles such as vinyl records.

EXAMPLES

The invention has been described with reference to various specific andpreferred embodiments and will be further described by reference to thefollowing detailed examples. It is understood, however, that there aremany extensions, variations, and modifications on the basic theme of thepresent invention beyond that shown in the examples and detaileddescription, which are within the spirit and scope of the presentinvention. All parts, percentages, ratios, etc. in the Specification andthe Examples are by weight unless indicated otherwise.

Example 1 and Comparative Examples 1-3

In order to evaluate the performance of an internally damped rotatablearticle a sample article was prepared by adding a layer of a 0.051 mmdamping material into the aluminum disk construction (Example 1) andcompared to the performance of a disk construction that was bondedtogether with a non-damping adhesive material adhesive (ComparativeExample 2), and a disk construction without a damping layer or adhesivelayer (Comparative Example 1).

Description of Sample

For the purpose of demonstrating the invention, an acrylic dampingmaterial was used in the damped disk build-up in a single layer. Thedamping material used was an acrylic polymer that had a loss factorgreater than 0.5 for a broad frequency range (±1000 Hz) at the desiredtest temperature (20° C./72° F.). The acrylic damping polymer selectedwas 3M Scotchdamp™ ISD-112, SJ2015 type 1202 available from MinnesotaMining and Manufacturing Company, St. Paul, Minn.).

Example 1

A 0.051 mm thick sheet of acrylic polymer damping material (3MScotchdamp™ ISD-112) was placed between two 68.26 mm diameter aluminumdisks, each having a 17.46 mm diameter center hole and a thickness of0.7112 mm, to form a construction. The acrylic polymer sheet completelycovered the inner surface of each aluminum disk. The construction wassubjected to hand pressure for about 1 minute and then rolled with a 4.5kg. roller to affect a bond between the acrylic polymer sheet and thetwo aluminum disks to provide an internally damped disk article.Although the disk article did not have any information storage layers webelieve, it is representative of a disk that would have such storagelayers.

The internally damped disk article was then tested as follows: Using aC-clamp, the internally damped disk article was secured at its center toa rigid table. The disk was then excited with an electromagnetictransducer (Electro 3030 HTB A) at a point 2 mm from its outer edgewhere a small piece of steel had been bonded. The resulting accelerationwas measured with an accelerometer (Endevco Model 22) at a pointdiametrically opposite to the excitation point and at 2 mm from itsouter edge. The transfer function was calculated from the accelerationmeasurement using a Tektronix 2630 Fourier Analyzer. Each transferfunction was the average of 100 measurements. The transfer function thusobtained is represented graphically as a function of frequency in FIG.5, as plot A.

The measurement of the damping is determined by calculating the systemloss factor for the disk article design at the desired resonantfrequency. The "system loss factor" is defined as: the width (Hz) of theresonant peak at 3 db below the resonant frequency of peak amplitude/theresonant frequency (Hz) at peak amplitude.

The system loss factor and the frequency are reported in Table 1 underEx. 1.

Comparative Example 1

In this comparative example, a laminate was prepared and tested as inExample 1 except that no acrylic polymer sheet was used and the twoaluminum disks were merely placed one on top of the other. The systemloss factor and the frequency are reported in Table 1 under Comp. Ex. 1.The C-clamp used in the test method served to hold the two diskstogether during testing.

Comparative Example 2

In this comparative example, a laminate was prepared and tested as inExample 1 except that a 0.0254 mm thick layer of non-dampingcyanoacrylate adhesive (Pronto™ Brand Instant Adhesive CA-8, availablefrom 3M Company) was used in place of the acrylic polymer sheet. Thetransfer function thus obtained is represented graphically in FIG. 5, asplot B. The system loss factor and the frequency are reported in Table 1under Comp. Ex.

                  TABLE 1                                                         ______________________________________                                        Example No.  Frequency (Hz)                                                                           System Loss Factor                                    Ex. 1        1850       0.243                                                 Comp. Ex. 1        2200               0.022                                   Comp. Ex. 2       2500                  0.020                                 ______________________________________                                    

From the data in Table 1 it can be seen that the system loss factor ofthe internally damped disk article (Ex. 1) is about 10 times greaterthan disk constructions of Comparative Examples 1 and 2 whichdemonstrates the superior damping performance of the internally dampeddisk article. FIG. 5 demonstrates the superior damping properties of alaminate representing the rotatable storage article of the inventioncompared to a laminate containing an internal adhesive layer which isnot a damping material.

The foregoing detailed description and example have been given forclarity of understanding only. No unnecessary limitations are to beunderstood therefrom. The invention is not limited to the exact detailsshown and described, for variations obvious to one skilled in the artwill be included within the invention defined by the claims.

What is claimed is:
 1. An internally damped rotatable storage article.Iadd.comprising.Iaddend.:.Iadd.a structural material selected from thegroup consisting of metals and ceramics; and.Iaddend. .[.having.]. atleast one layer of vibration damping material contained therein,comprising a viscoelastic material, said vibration damping materialhaving a loss factor of at least about 0.01 and a storage modulus of atleast about 6.9×10³ Pascals, wherein the thickness of each of saidlayer(s) ranges from about 0.002 mm to about 0.5 mm, and wherein thevibration damping is improved by at least about 10% in at least 1vibrational mode.
 2. The rotatable storage article of claim 1 whereinthe thickness of each of said layer(s) ranges from about 0.002 mm toabout 0.15 mm.
 3. The rotatable storage article of claim 1 wherein thethickness of each of said layer(s) ranges from about 0.002 mm to about0.05 mm.
 4. The rotatable storage article of claim 1 wherein thethickness of each of said layer(s) of vibration damping material isabout 0.5 to about 50% the thickness of the article.
 5. The rotatablestorage article of claim 1 wherein the thickness of each of saidlayer(s) of vibration damping material is about 1 to about 25% thethickness of the article.
 6. The rotatable storage article of claim 1wherein the viscoelastic material has a loss factor greater than about0.1 and a storage modulus of at least about 6.9×10⁴ Pascals.
 7. Therotatable storage article of claim 1 wherein the viscoelastic materialhas a loss factor of 0.5 to about 10 and a storage modulus of about6.9×10⁴ to about 1.4×10⁷ Pascals.
 8. The rotatable storage article ofclaim 1 wherein the viscoelastic material is selected from the groupconsisting of thermoplastic polymers, thermosetting polymers, andmixtures thereof.
 9. The rotatable storage article of claim 1 whereinthe viscoelastic material is a thermosetting polymer.
 10. The rotatablestorage article of claim 9 wherein the thermosetting polymer is anacrylate.
 11. The rotatable storage article of claim 1 selected from thegroup consisting of magnetic rotatable storage articles.[., opticalrotatable storage articles, magneto-optical rotatable storagearticles,.]. and mechanical rotatable storage articles.
 12. Therotatable storage article of claim 1 selected from the group consistingof magnetic rigid disks, magnetic floppy disks, magnetic drums,.[.optical compact disks, optical disks, optical drums, magneto-opticalcompact disks, magneto-optical disks, magneto-optical drums.]. and vinylrecords.
 13. The rotatable storage article of claim 1 wherein saidrotatable storage article contains at least 2 layers of vibrationdamping material.
 14. The rotatable storage article of claim 1 whereinthe vibration damping material further comprises a fibrous material. 15.The rotatable storage article of claim 14 wherein the vibration dampingmaterial includes about 3 to about 60 weight percent fibrous material,based on the total weight of the vibration damping material.
 16. Therotatable storage article of claim 1 wherein the vibration dampingmaterial further comprises a particulate material.
 17. The rotatablestorage article of claim 16 wherein the particulate material is selectedfrom the group consisting of glass bubbles, glass beads, ceramicbubbles, ceramic beads, thermally conductive bubbles, aluminum oxidepowder, aluminum nitride powder, silica, and cured epoxy nodules. 18.The rotatable storage article of claim 1 wherein the vibration dampingmaterial includes about 0.5 to about 70 weight percent of particulatematerial based on the total weight of the vibration damping material.19. The rotatable storage article of claim 1 wherein the vibrationdamping material further comprises a fibrous material and a particulatematerial.
 20. The rotatable storage article of claim 1 which contains asingle layer of vibration damping material wherein said layer ispositioned within the article at a distance of at least about 5% of thethickness of the article from an upper and lower surface of the article.21. The rotatable storage article of claim 1 which contains a singlelayer of vibration damping material wherein said layer is positionedwithin the article at a distance of at least about 30% of the thicknessof the article from an upper and lower surface of the article.
 22. Therotatable storage article of claim 1 wherein the rotatable storagearticle has one layer of damping material positioned equidistant from anupper surface of the article and a lower surface of the article.
 23. Therotatable storage article of claim 1 which contains at least two layersof vibration damping material wherein each damping material layer ispositioned within the article such that it is at least about 5% of thethickness of the article away from an upper and lower surface of thearticle and each vibration damping material layer is at least about 5%of the thickness of the article away from another vibration dampinglayer.
 24. The rotatable storage article of claim 1 which contains atleast two layers of vibration damping material wherein each dampingmaterial layer is positioned within the article such that it is at leastabout 5% of the thickness of the article away from an upper and lowersurface of the article and each vibration damping material is at leastabout 20% of the article thickness away from another damping layer. 25.The rotatable storage article of claim 1 which contains at least twolayers of vibration damping material wherein each damping material layeris positioned within the article such that it is at least about 5% ofthe thickness of the article away from an upper and lower surface of thearticle and each vibration damping material is at least about 30% of thearticle thickness away from another damping layer.
 26. The rotatablestorage article of claim 1 wherein the vibration damping materialfurther comprises an epoxy resin material, wherein said epoxy resinmaterial may optionally have vibration damping properties.
 27. Therotatable storage article of claim 1 wherein the vibration damping layeris a continuous layer.
 28. The rotatable storage article of claim 1wherein the vibration damping layer is a continuous layer made up ofadjacent sections of different vibration damping materials.
 29. Therotatable storage article of claim 1 wherein the article contains atleast 2 layers of vibration damping material, wherein at least 2 of thelayers comprise different damping materials.
 30. The rotatable storagearticle of claim 1 wherein the vibration damping layer is adiscontinuous layer.
 31. The rotatable storage article of claim 30wherein the discontinuous layer comprises sections of damping materialseparated by non-damping material or spaces.
 32. The rotatable storagearticle of claim 1 wherein each vibration damping material layer isencased within the storage article.
 33. A method of improving theviscoelastic damping characteristics of a rotatable storage article.Iadd.comprising a structural material selected from the groupconsisting of metals and ceramics, the method .Iaddend.comprisingproviding at least one layer of vibration damping material within therotatable storage article, each vibration damping material layercomprising a viscoelastic material, said vibration damping materialhaving a loss factor of at least about 0.01 and a storage modulus of atleast about 6.9×10³ Pascals, wherein the thickness of each of saidlayer(s) ranges from about 0.002 mm to about 0.5 mm, and wherein thevibration damping is improved by at least about 10% in at least 1vibrational mode. .Iadd.34. An internally damped rotatable storagearticle having at least one layer of vibration damping materialcontained therein, comprising a viscoelastic material, said vibrationdamping material having a loss factor of at least about 0.01 and astorage modulus of at least about 2.0×10⁵ Pascals, wherein the thicknessof each of said layer(s) ranges from about 0.002 mm to about 0.5 mm, andwherein the vibration damping is improved by at least about 10% in atleast 1 vibrational mode..Iaddend..Iadd.35. The rotatable storagearticle of claim 1, wherein the article is a magnetic rotatable storagearticle..Iaddend..Iadd.36. A disk drive comprising the rotatable storagearticle of claim 1..Iaddend..Iadd.37. A computer comprising the diskdrive of claim 36..Iaddend..Iadd.38. A disk drive comprising therotatable storage article of claim 34..Iaddend..Iadd.39. A computercomprising the disk drive of claim 38..Iaddend..Iadd.40. A disk drivecomprising:an internally damped magnetic rotatable storage articlecomprising: at least one layer of vibration damping material comprisinga viscoelastic material contained therein, said vibration dampingmaterial having a loss factor of at least about 0.01 and a storagemodulus of at least about 6.9×10³ Pascals, wherein the thickness of eachof said layer(s) ranges from about 0.002 mm to about 0.5 mm, and whereinthe vibration damping is improved by at least about 10% in at least 1vibrational mode..Iaddend..Iadd.41. A computer comprising the disk driveof claim 40..Iaddend..Iadd.42. The disk drive of claim 40, wherein theinternally damped magnetic rotatable storage article comprises a glassstructural material..Iaddend..Iadd.43. The internally damped rotatablestorage article of claim 1, wherein the structural material ismetal..Iaddend.